1. Field of the Invention
The present invention relates to a process for producing a skin material-laminated foamed thermoplastic resin molding and to foamed thermoplastic resin moldings. More particularly, the invention is directed to a process for producing a panel-shaped foamed thermoplastic resin molding having a skin material laminated, the molding being lightweight, highly rigid and suitable for automotive interior parts, and to products obtainable by the process and the like.
2. Description of the Related Art
Skin material-laminated thermoplastic resin moldings which are produced by molding a thermoplastic resin by injection molding or the like and also providing a skin material on the surface of the molded resin and which are used for automotive interior parts or the like are conventionally employed. Such moldings, however, have high densities and high weights, so there are demands for reduction in weight and improvement in quality particularly in the field of automotive interior parts. In particular, there is a strong demand for improvement in external quality even for the back sides of skin material-laminated moldings.
As automotive interior parts, a technique in which a skin material is laminated and weight reduction is ensured through the use of a foamed thermoplastic resin whose inner layer is a foamed layer is known in Japanese Patent Kokai Publications Nos. 6-344362 and 4-148907.
In the above publications, the mold stamping molding method is disclosed. In other words, a technique of molding is disclosed, the technique comprising setting a skin material between a pair of an upper and lower mold members, making the clearance between the mold members to be a specific value, injecting a foaming agent-containing polypropylene resin composition to between the skin material and the lower mold member and simultaneously closing the mold members, thereby forming the resin into a predetermined shape and bonding the resin to the skin material, then opening the mold members, thereby foaming the resin, and then cooling and solidifying the resin.
In the technique disclosed in the above publications, the injection of a resin is executed with the clearance between the mold members widened in order to reduce resin supply pressure. This results in insufficient prevention of the evaporation of a foaming agent, the so-called gas escape, that occurs during the injection of a foaming agent-mixed molten resin into the mold. This causes appearance failure in the back surface of a substrate due to the gas escape and, therefore, the substrate with a skin material laminated thereon has unsatisfactory appearance in its back surface.
The object of the present invention is to provide a process for producing a skin material-laminated foamed thermoplastic resin molding by which the evaporation of a foaming agent, the so-called gas escape, that occurs during the injection of a molten resin into a mold can be sufficiently prevented and, as a result, a foamed layer is surely formed and by which a foamed thermoplastic resin molding having good external appearance in its anti-skin material-laminated side, namely the side of the substrate in the molding reverse to its skin material-laminated surface, and to provide products obtainable by the process and the like.
The present inventors studied a technique for preventing the gas escape from a foaming agent-containing molten thermoplastic resin with in stamping molding. To make a resin supply clearance of a mold wide in order to greatly reduce the required injection pressure to inject a molten resin in comparison with general injection molding is considered to be an essential feature of the conventional stamping molding. In contrast to this, after finding that the gas escape can be effectively prevented through setting the specific resin supply clearance which is relatively smaller than that at which stamping molding cannot be conducted because of high resin injection pressure required, the present inventors have reached the present invention.
That is, the present invention is a process for producing a foamed thermoplastic resin molding comprising a skin material and a thermoplastic resin foam integrally laminated with the skin material, wherein the process uses a mold comprising a male and female mold members which are mutually slidable and whose cavity clearance (t) is adjustable, the process comprising the following steps (1)-(5):
(1) skin material supply step for supplying a skin material with the female and male mold members opened;
(2) resin injection step including bringing the male mold member and the female mold member close mutually to make the t to be a resin injection clearance less than (C+5) mm (C is the thickness of the skin material before molding), and injecting a foaming agent-containing molten polyolefin-based resin through a resin supply opening provided in one of the male and female mold members to between the skin material and the mold member;
(3) compression step for shaping the injected polyolefin-based resin by filling up it to an end of a mold cavity by making the t smaller than the resin injection clearance by compression, and simultaneously laminating the skin material integrally with the polyolefin-based resin;
(4) foaming step for forming a foamed thermoplastic resin molding by forming a foamed layer through foaming the polyolefin-based resin injected in its molten state through enlarging the t after the completion of the shaping of the polyolefin-based resin; and
(5) cooling and releasing step including cooling the foamed thermoplastic resin molding in the mold, then opening the mold and taking out the foamed thermoplastic resin.
The execution of the above steps results in the sufficient prevention of the evaporation of a foaming agent during the injection of a foaming agent-containing molten resin into a mold, resulting in the certain formation of a foamed layer and enabling foamed thermoplastic resin moldings with excellent external appearance in their anti-skin material-laminated surfaces of their substrates to be produced.
Particularly, letting the resin injection clearance of the mold in resin supply step (2) be less than (C+5) mm, at which clearance it was heretofore thought to be impossible to conduct molding successfully by stamping molding due to too high resin injection pressure, can effectively prevent a gas to escape and can shorten the time required for the opening and closing movement of a mold after the injection of a molten thermoplastic resin.
As the skin material to be used in the present invention can be employed various kinds of skin materials having a single layer or a plurality of layers such as those conventionally used. In the case of using a skin material having a cushion layer laminated as a multiple-layered skin material, it is desirable to use a skin material having a cushion layer with a compression modulus of not greater than 0.3 MPa and it is required to provide a backing layer that will serve as a protective layer of the cushion layer.
The panel-shaped foamed thermoplastic resin molding, which is the product of the present invention, can be suitably used particularly for automotive interior parts, specific examples thereof including instrument panels, seat backs, partition boards, console boxes and door trims.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
Throughout this specification and the claims which follow, unless the context requires otherwise, the word xe2x80x9ccomprisexe2x80x9d, and variations such as xe2x80x9ccomprisesxe2x80x9d and xe2x80x9ccomprisingxe2x80x9d, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integer or step.